Heat responsive marking sheets



y 1965 M. F; BAUMANN ETAL 3,185,583

HEAT RESPONSIVE MARKING SHEETS Filed Nov. 19, 1962 CO- CRYSTAL ADDUCT OF A HIGHLY BASIC AMINE AND A HYDROXYPHENOL COMPOUND :LEWIS ACID COMPLEX OF AN AMINE AND A STANNOUS SALT SUPPORT INVENTORS MICHAEL E BAUMANN WILLIAM R.LAWTON ATTORNEYS United States Patent l 3,185,583 HEAT RESPONSIVE MARKING SHEETS Michael F. Baumann, Hudson, and William R. Lawton, Nashua, NH, assignors to Nashua Corporation, Nashua, N.H., a corporation of Delaware Filed Nov. 19, 1962, SenNo. 238,711 5 Claims. (Cl. 11736.8)

This invention relates/to thermographic copying sheets and is particularly concerned with a copy sheet which is characterized by its ability to form a colored image of a color contrasting to the background wherever the sheet is exposed to heat.

' The exposure may be made through a master copy which is exposed to radiant energy. That energy is converted to sensible heat in the indicia appearing on the master sheet. Consequently the copy sheet is subjected to selective, localized heating under the indicia and a colored image of the original indicia appears. In recording apparatus, the sheet is heated directly by a hot stylus.

For brevity, both such modes of heating will be referred to as the thermographic process.

The present invention is a continuation of work begun in the applications of William R. Lawton and Eugene F. Lopez, Serial No. 808,012, filed April 22, 1959, now U.S. Patent No. 3,076,707, and the application of William R.

3,185,583 Patented May 25, 1965 "ice in thermographic apparatus (50 to 150 C.) in the absence of the Lewis acid type complex.

The reaction is apparently controlled by temperature and basicity, for the specific carrier compound-and hence the specific temperature at whichthe amine is released from its co-c'rystalline relationship with the carrier-appears to have little to do with the response.

Accordingly one carrier, i.e., a compound reactive with the amine to form the co-crystal adduct, namely tetrachlorobisphenol-A (which is chemically 4,4-isopropylinenebis-(2,6-dichlorophenol) is chosen and may be considered as a typical example of the great variety of known amine carriers.

Only highly basic amines when released from the carrier appear to be effective in promoting the reaction. Such amines include hydrazine, 1,3-propylenediamine, tetramethylquanadine, ethanolamine, diethylenetriamine, polyglycolamine, tetraethylenepentamine, triethylenetetraamine, triethanolamine, and diethanolamine.

Many Lewis type acid complexes have been tested and of these the most effective appears to be the stannous chloride-amine Lewis acid type complex. The stannous Lawton (sole) Serial No. 206,186, filed June 29, 1962, 1

both of which are assigned to the assignee of this invention. The entire disclosure of both above identified applications is herein incorporated by reference.

The above applications disclosed that the co-crystal adducts of a bisphenol and an amine, or an hydroxyphenol substituted chroman and an amine can be coated on a copy sheet where they remain inert and non-reactive. When heated to between 50 and 150 C., however, these complex crystals .dissociate,'releasing the amine which thereupon can react with materials with which it is in intimate contact. In the two applications mentioned above, one such material is an 2120 compound which is developed or changed'in color by the amine which has been released by the heat of the thermographic process.

As a class, the co-crystal adducts of bisphenols are well known. Many are described in U.S. Patent 2,829,175. The hydroxyphenol substituted chroman co-crystal adducts are described by Crarner, Einschlussverbindungen (published by Springer-Verlay, Berlin, 1954) We have now discovered that upon the release of a highly basic amine from a co-crystal by the heat of the thermographic' process, a colored image will be produced whenever two other potential reactants are present in the coating-namely, a thiosulfate of copper or lead, and a Lewis acid type complex formed from the combination of equimolar proportions of a tin salt such as stannous chloride and an organic amine such as triethanolamine.

Other amines may be substituted in the complex, such as ethanolamine, diethanolamine, piperidine, and isobutylamine, but in general, the response will be at a somewhat higher temperature.

The color forming from the heating of the coating appears to be the result of the decomposition of the thiosulfate and the appearance of a colored sulfide. The promoter of this reaction appears to be the amine freed from the co-crystal by such heating.

A reaction which forms an acceptable colored image will not take place at temperatures which are practicable manner.

sulfate-amine complex also gives acceptable results. The Lewis acid is formed by dissolving equal mole ratios of the tin salt and amine in water. A precipitate of the complex forms and is recovered by filtration.

The accompanying drawing illustrates schematically a heat sensitive sheet corresponding to this invention. The

sheet is represented as being in cross section.

PREPARATION OF THE BISPHENOL/AMINE ADDUCT Example 1 The solid molecular complex adduct of tetrachlorobisphenol A and diethanolamine is prepared in the following 1 mole (366 grams) of tetrachlorobisphenol A is dissolved in 1098 grams of toluol with heat. To this solution is added 2 moles (210 grams) of diethanolamine with constant agitation. A fine crystalline precipitate is obtained and the crystals are collected by filtering and are washed three times with normal hexane and allowed to dry. The product is the adduct-tetrachlorobisphenn A/diethanolamine (TCBA/ DEA) Example 2 (A) Ten parts by weight of lead thiosulfate (PbS O is ball-milled in parts of a 2 /z% solution of polyvinylbutyral (Butvar-76) in trichloroethylene until it is reduced to an appropriate particle size.

(B) Ten parts of the tin salt complex stannous chloride-diethanol-amine (produced as above) is ground in 90 parts of a 2 /2% solution of polyvinylbutyral in trichloroethylene to appropriate size.

(C) Ten parts of the co-crystalline adduct of tetrachlorobisphenol-A and diethanolamine (TCBA/DEA) are ball-milled in 90 parts of a 2 /z% solution of polyvinylbutyral in trichloroethylene until the proper size is reached. Thereafter the three dispersions are combined with stirring in the ratios of solid ingredients given below.

Dispersion (C) 4 The resulting mix is coated on a suitable carrier, i.e., thin paper having a ream weight of 22 lbs. per ream of 24" x 26 x 500 sheets. The coating is spread by conventional machinery to a dry weight of about lbs. per ream. The coating is then dried and is responsive to thermographic heating to produce a distinctly colored image.

Following the procedure of Example 2, other coating mixes were made with ingredients and proportions which follow:

tive, produces a yellow background which sometimes is objectionable. These compositions when coated on a support as described in Example 2 produce a colored image when exposed to heat in thermographic apparatus.

PREPARATTON OF THE CHROMAN ADDUCTS Example 6 A hydroxyphenol substituted chroman, namely 2'-.hydroxy-2,4,4,7,4'-pentamethyl flavan is prepared according to a procedure described by Baker and Besley in J. Chem. Soc., 1951, 1102-6. A mixture of m-cresol (440 g.) and acetone is saturated with gaseous HCl without cooling and kept at 40 C. for two days with the exclusion of water. The dark product is added to an excess of 20% sodium hydroxide solution, a layer of ether is poured on the surface, and the mixture is vigorously stirred causing the ether addition product of the dimeride to crystallize. After standing overnight in an open vessel the solid is collected, Washed thoroughly with water, dissolved in hexane, and dried with calcium chloride. The solution is filtered and a small amount of ether is added to the solution. The ether complex of the flavan compound separates in large, colorless, thick rhombic prisms having a melting point of 7677 C. A flavan co-crystal adduct is prepared by mixing fifteen parts of a 10% hexane solution of the flavan ether complex with 7.5 parts of dicyclohexylamine, chilling the mixture overnight, and filtering the solid crystalline adduct product, M.P. 103-105 C.

While the above flavan material is one which we have found to be effective in the formation of numerous cocrystal adducts which exhibit dissociation temperatures within the range of about 50-150 C. it is not the only available or useful hydroxyphenol substituted chroman. Numerous other hydroxyphenol substituted chromans may be used and among these which we prefer are 7,4-diethyl-2'-hydroxy-2,4,4-trimethyl flavan; cyclohexanespiro- 4-(2-hydroxy-7,4'-dimethyl-2,3 tetramethylene) flavan; 2' hydroxy-2,4,4,6,7,4',5-heptamethyl flavan; 2'-hydroxy- 2,4,6 ,5-pen tamethyl fiavans; 4-p-hydroxyphenyl-2,2,4-trimethyl chroman. As in the case of the bisphenols, many amines are suitable, the most effective being the alcohol amines. The chroman adducts can normally be prepared by simple mixing of the selected chroman and amine in the manner shown above.

The hydroxyphenol substituted chroman adducts may be substituted for the bisphenol adducts of the preceding examples with substantially the same result, but because of their Water insensitivity it is convenient, at times, to apply a first coat containing only the chroman adduct suspended in a water solution of a water-soluble binder, e.g., polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose or gums. In such cases, the aqueous first coat which is applied to the supporting sheet at the dry weight of approximately 4- lbs. per ream of 24" x 26" x 500 sheets may be as follows:

Example 7 Parts 2' hydroxy-2,4,4,7,4-pentamethyl flavan/ethylenediamine 20 Polyvinyl alcohol 2 Water 98 When the coating is dry it is overcoated to a dry weight of about 2 lbs. per ream of a coating composition comprising the mixture of equal parts of dispersion (A) of Example 2 and dispersion (B) Example 2. When the second coat is dry the sheet is responsive to thermographic heating to produce a distinctly colored image.

Additional heat responsive sheets may be prepared in a similar manner by overcoating with compositions comprising mixtures of the dispersions (A) and (B) in combination as set forth in Examples 3, 4, and 5 above.

What is claimed as the present invention is:

1. A heat-responsive copy sheet adapted to change visibly to a contrasting color wherever subjected to localized heating to a temperature of between 50 and C. comprising, in combination,

(a) a supporting sheet carrying on a surface thereof a coating comprising a uniformly distributed intimate association of finely divided particles of (b) a thiosulfate of a metal selected from the class consisting of copper and lead,

(0) a solid, normally stable, co-crystal adduct comprising the reaction product of a highly basic amine and an hydroxyphenol compound selected from the class consisting of bisphenols and hydroxyphenol substituted chromans, and which is heat dissociable in the temperature range of 50 C.1 50 C., and

(d) a Lewis acid type complex comprising the reaction product of a tin salt selected from the group consisting of stannous chloride and stannous sulfate and an amine.

2. A heat-responsive copy sheet as claimed in claim 1 wherein the thiosulfate is lead thiosulfate, the co-crystal adduct is the adduct of tetrachlorobisphenol-A and diethanolamine, and the Lewis acid type complex is the complex formed by equimolor proportions of stannous chloride and diethanolamine.

3. A heat-responsive copy sheet as claimed in claim 1 wherein the Lewis acid type complex is the complex formed by equimolar proportions of stannous sulfate and triethanolamine.

4. A heat-responsive copy sheet as claimed in claim 1 wherein the thiosulfate is copper thiosulfate, the Lewis acid type complex is the complex formed by equimolar proportions of stannous sulfate and tributylamine, and the co-crystalline adduct is the adduct of tetrachlorobisphenol-A and tributylamine.

5. A heat-responsive copy sheet as claimed in claim 1 wherein the thiosulfate is lead thiosulfate, the co-crystal adduct is the adduct of 2'-hydroxy-2,4,4,7,4'-pentamethy1 fiavan/ethylenediamine, and the Lewis acid type com- 3, 185,583 5 plex is the complex formed from equimolar proportions 2,995,466 of stannous chloride and diethanolamine. 3,024,362 3,03 1,329 References Cited by the Examiner 3,076,707

UNITED STATES PATENTS 2,813,042 11/57 Gordon et a1. 11736.8'

Sorensen 117-36.8 Sus et a1. 117-36.8 Wingert 117-36.8 Lawton et a1. 1l7-36.8

5 WILLIAM D. MARTIN, Primary Examiner.

RICHARD D. NEVIUS, MURRAY KATZ, Examiners. 

1. A HEAT-RESPONSIVE COPY SHEET ADAPTED TO CHANGE VISIBLY TO A CONTRASTING COLOR WHEREVER SUBJECTED TO LOCALIZED HEATING TO A TEMPERATURE OF BETWEEN 50* AND 150*C. COMPRISING, IN COMBINATION, (A) A SUPPORTING SHEET CARRYING ON A SURFACE THEREOF A COATING COMPRISING A UNIFORMALY DISTRIBUTED INTIMATE ASSOCATION OF FINELY DIVIDED PARTICLES OF (B) A THISULFATE OF A METAL SELECTED FROM THE CLASS CONSISTING OF COPPER AND LEAD, (C) A SOLID, NORMALLY STABLE, CO-CRYSTAL ADDUCT COMPRISING THE REACTION PRODUCT OF A HIGHLY BASIC AMINE AND AN HYDROXYPHENOL COMPOUND SELECTED FROM THE CLASS CONSISTING OF BIDPHENOLS AND HYDROXYPHENOL SUBSTITUTED CHORMANS, AND WHICH IS HEAT DISSOCIABLE IN THE TEMPERATURE RANGE OF 50*C.-150*C., AND (D) A LEWIS ACID TYPE COMPLEX COMPRISING THE REACTION PRODUCT OF A TIN SALT SELECTED FROM THE GROUP CONSISTING OF STANNOUS CHLORIDE AND STANNOUS SULFATE AND AN AMINE. 